When the Okavango River, a dark green ribbon cutting through the Angolan Highlands, reaches the Kalahari Desert in Botswana it branches out into a fan-shaped network of veins that forms the lush Okavango Delta.

A UNESCO World Heritage site, the delta covers about 5,791 square miles in northern Botswana. The oasis is home to more than 2,000 species of animals and plant life, including elephants, rhinoceroses and the endangered African wild dog. Described as “Africa’s last Eden,” it draws thousands of visitors annually.

But recently, conservationists came across a disturbing discovery near the famed wildlife sanctuary: the bodies of 87 elephants, many of which bore brutal injuries consistent with their being killed for their tusks.

“I’m shocked, I’m completely astounded,” Mike Chase, founder of the conservation group Elephants Without Borders, told the BBC. “The scale of elephant poaching is by far the largest I’ve seen or read about anywhere in Africa to date.”

On Tuesday, the Botswana government issued a statement disputing the group’s claims, calling the statistics “false and misleading.”

According to the statement, Elephants Without Borders only reported seeing 53 elephant carcasses while conducting aerial wildlife surveys supported by the government between July and August. An additional “verification mission … established that the majority were not poached but rather died from natural causes and retaliatory killings as a result of human and wildlife conflicts,” the statement said.

Chase told National Geographic each of the 87 dead elephants has a GPS location and every survey flight had four people aboard the plane, including a government employee. Voice recordings were also taken during the flights, Chase said.

“I am an objective scientist, with no political agenda,” he said. “I am sad that our government has responded in this way.”

Botswana is home to one of the largest elephant populations in Africa, more than 130,000, according to the Great Elephant Census, which is considered to be the largest wildlife survey in history. The census found about 350,000 elephants in 18 African countries.

In a tweet Monday, Elephants Without Borders described the recent rate of poaching as “alarming.”

“When I compare this to figures and data from the Great Elephant Census, which I conducted in 2015, we are recording double the number of fresh poached elephants than anywhere else in Africa,” Chase told BBC.

An elephant carcass is described a “fresh” when it is killed within the past three months, but a majority of the elephants found near the delta died in recent weeks, NPR reported, citing an Elephant Poaching Incident Report Reference written by Chase.

According to the report, all the carcasses were “presumed to be poached” because “all of them had their skulls chopped to remove their tusks.” The wide range of classification and age of the dead elephants indicated a “poaching frenzy” that “has been ongoing in the same area for a long time.”

Poachers had attempted to conceal the “mounds of rotting flesh” with drying bushes, the report said.

In addition to the elephants, five white rhinoceroses had also been poached from the area in recent months, the BBC reported.

About four months ago in May, the government made a controversial to disarm Botswana’s anti-poaching unit, just one month after President Mokgweetsi Masisi was sworn into office, according to the BBC. It’s a move that goes against Botswana’s former policy against poachers, which had garnered praise from conservationists for its “shoot to kill” stance.

“People did warn us of an impending poaching problem and we thought we were prepared for it,” Chase told the BBC.

He added: “The poachers are now turning their guns to Botswana. We have the world’s largest elephant population and it’s open season for poachers.”

In its statement, officials also pushed back against the notion that taking weapons away from the Department of Wildlife and National Parks’s (DWNP) anti-poaching unit contributed to the rise in poaching.

Since the 1980s, the country has instructed all its security agencies to take part in the anti-poaching effort, a practice that is still ongoing, the statement said.

The recent decision, the government said, “has not created any vacuum in anti-poaching operations as the anti-poaching unit in DWNP continues to play a pivotal role in combating wildlife crime through other strategic interventions.”

Given the country’s harsh anti-poaching policies, Botswana has long been known as a place where wildlife can thrive, largely free from human threats.

In a 2013 documentary created by British actor and filmmaker Tom Hardy, Chase described the area’s elephants as “political refugees.”

“They fled to the safety and security of Botswana, moving away from poaching,” he said at the time.

In the same series, Tshekedi Khama, Botswana’s minister of environment, wildlife and tourism, explained the country’s low tolerance for poachers to Hardy as the pair discussed the black market ivory trade, focusing specifically on its popularity in Asia.

“It’s a culture. We have to kill the supply to starve the culture,” Khama said. “That is one of the reasons why, in Botswana, with our anti-poaching unit, we don’t necessarily interrogate the poacher. And that is a position we’ve adopted to send a clear message to say, ‘If you want to come and poach in Botswana, one of the possibilities is you may not go back to your country alive.’ ”

The policy also applied to locals, Khama said, adding that even if poachers put their weapons down, they would still be shot.

That same year, the government led by then-President Ian Khama, Tshekedi Khama’s brother, also issued a ban on hunting of wildlife after aerial surveys showed a decline in the number of wild animals, the Sunday Standard reported.

This summer, officials announced they would begin reviewing the hunting ban after the country’s parliament called on the government in June to consider lifting the ban in areas not designated as game reserves or national parks.

The recent moves to roll back the policies protecting Botswana’s wildlife is not sitting well with conservationists.

“Botswana has always been at the forefront of conservation and it will require political will,” Chase told BBC, noting that the recent rash of poaching-related deaths “requires urgent and immediate action by the Botswana government.”

“Our new president must uphold Botswana’s legacy and tackle this problem quickly,” he said. “Tourism is vitally important for our economy, jobs, as well as our international reputation, which is at stake here as being a safe stronghold for elephants.”

On social media, news of the elephants’ untimely deaths was met with fierce outrage.

This Is Africa, a local English-language magazine, tweeted at Masisi, demanding the government take action.

“A month after you were sworn in you disarmed the anti-poaching unit. Why?” the Monday tweet said. “Save the elephants in Botswana and stop the poaching. Botswana is the last refuge for these elephants and they must be conserved.”

American celebrities, including actress and singer Vanessa Williams, also chimed in. Williams posted a graphic photo of one of the dead elephants to Instagram, writing, “Botswana WAS the last sanctuary of hope for our precious wildlife with a government that used to understand that value of protecting our wildlife.”

Some were even reminded of President Donald Trump’s recent decision to lift the U.S. ban on importing tusks and other elephant body parts as hunting trophies. In March, the U.S. Fish and Wildlife Service said in a memorandum that the agency would issue sport hunters permits for trophy items on a “case-by-case basis,” The Washington Post’s Eli Rosenberg reported.

In response to the backlash, the Botswana government remained unwavering.

“The Government of Botswana wishes to condemn in the strongest terms possible attempts by individuals or groups who give a false impression that they love Botswana wildlife more than citizens of Botswana,” the statement said. “Government wishes to reiterate the fact that wildlife remains a national heritage and our citizens will protect it at all costs.”